This invention relates to a device for grinding a rotary mower blade. The invention also provides a method of grinding a rotary mower blade.
Rotary mowers operate by having substantially planar blade rotating about its midpoint in a plane substantially parallel with the ground over which the mower is running. The blade is provided with cutting edges which extend from one distal end to the center point of the blade, and from the opposite distal end to the mid-point on the opposite blade edge. A sharp edge must be provided for the grass to be cut efficiently.
The initial grinding of the blade to form the cutting edge, and the subsequent regrinding to restore the cutting edge is often carried out by eye using an angle grinder. Clearly, this often leads to an uneven cutting edge, and is time consuming to carry out.
U.S. Pat. No. 5,218,787 to Rice discloses apparatus to be used in conjunction with a bench grinder for use in sharpening mower blades. The apparatus has conventional overcentre gripping pliers mounted on an adjustable carriage to hold the blade.
The present invention seeks to provide an efficient and easily adjustable means for grinding rotary mower blades advantageous over the prior art in that it provides a more accurate and a consistent grind along the whole length of the blade thus minimising the need for subsequent balancing. The invention can also grind the cutting edge of blades at an angle from the longitudinal axis of the blade more quickly and more safely than prior art grinding devices, as it can be operated entirely hands free.
One aspect of he present invention provides a device for grinding a rotary mower blade which device comprises an adjustable support for receiving a rotary mower blade, means for fixing the blade relative to the support, means for feeding the support and blade both axially and transversely relative to a grinding wheel and for pivoting the support towards and away from the grinding wheal, wherein the fixing means is adapted to secure the blade in a first grinding position for grinding one edge of the blade, but in use enables the blade to be released from the first grinding position, turned about a substantially central point of the blade and re-secured in a second grinding position so as to grind the opposite edge of the blade.
According to one optional feature of the invention, the adjustable support comprises a fixed element and a slidable element. Preferably, the sliding element includes a longitudinal slot and the fixed element includes locking means slidable along said slot to adjust the support to a selected overall length.
In another optional feature of this aspect of the present invention the fixing means comprises a cone secured to the slidable element and a magnet secured to the fixed element wherein the cone locates in an aperture in the centre of the blade. Preferably, the magnet is an electromagnet.
A further optional feature provides that the adjustable support is mounted on a carriage for axial and transverse feeding. Preferably, the carriage is mounted on a slide extending perpendicular to the axis of the grindstone for transverse feed. Even more preferably, the transverse feed is controlled by means of a hand wheel attached by a feed screw to said carriage.
A yet further optional feature provides that the carriage is mounted on a slide extending parallel to the axis of the grindstone for axial feed. Optionally, the axial feed may be manually operated.
Alternatively, the axial feed may be automatically operated.
According to another optional feature the support pivots about an axis perpendicular to the axial and transverse feed directions. Preferably, the support pivots about and axis in line with the centre of the magnet mounted on said support.
Optionally, the support may pivot about a selected one of a plurality of available positions on the carriage.
Optionally, the angle of pivot may be set by an adjustable and reversible side stop.
A yet further optional feature provides that the carriage may be fitted with adjustable limit stops for both axial and transverse feed directions.
Another optional feature provides that an additional grindstone attached to an additional motor may be provided such that both sides of blade may be ground simultaneously. Preferably, the or each grindstone is adjustable in height relative to the support.
A second aspect of the present invention comprises a method of grinding a rotary mower blade comprising securing the blade to an adjustable support, adjusting a side stop to set the grinding angle of the blade, setting the transverse feed position using a band wheel, setting the height of a grinding stone relative to the blade, axially feeding the blade past the grindstone until the grinding of one side is complete, releasing the blade from the adjustable support, rotating the blade through substantially 180xc2x0, resecuring the blade to the adjustable support, and grinding the opposite side of the blade.